Led backlight for display systems

ABSTRACT

An LED backlight method and apparatus for display systems provides a plurality of light emitting diodes having different white point colors. At least two of the light emitting diodes having different white point colors are selected to produce a light of a predetermined white point color when the light outputs of the selected light emitting diodes are mixed. The selected light emitting diodes are mounted on a display panel in a predetermined order at spatially distributed positions for mixing their light outputs to produce the light of the predetermined white point color to illuminate the display panel with the light of the predetermined white point color.

TECHNICAL FIELD

The present invention relates generally to device display systems, andmore particularly to an LED backlight with highly uniform color forilluminating display systems.

BACKGROUND ART

As computer technology has advanced, the demand for portable computersystems, such as laptops, has increased. Portable computers havedramatically increased the mobility of computing power for the computeruser. Since the first portable computer, manufacturers have increasedcomputer mobility by decreasing the size, weight, and power demands ofportable computers, increasing battery life, and increasing performance.

The monitors presently used contribute greatly to the overall size andweight of the portable computer. The monitor must be of a sufficientsize, brightness, and clarity to provide the user with readable images.In order to achieve these requirements, monitors place a large demand onavailable power resources and are therefore a significant contributorindirectly as well as directly to the weight of the portable computer.

Typically, portable computer monitors utilize a liquid crystal displaysystem. The liquid crystal display systems typically include a topplastic or glass panel and a bottom plastic or glass panel, having aliquid crystal display of thin film transistors and liquid crystalmaterial in between. These systems also utilize a backlight system thattypically includes a diffuser for passing light evenly to the liquidcrystal display, a cold cathode fluorescent lamp (“CCFL”) for producinglight, a reflector for directing the light toward the diffuser, and alight pipe located between the diffuser and the reflector to spreadlight to the entire surface of the diffuser.

The use of conventional CCFL liquid crystal display systems in themonitors of portable computers, however, creates a limiting factor inthe continuing effort to reduce the size and weight of portablecomputers. CCFL technology has not kept pace with advances in othertechnologies that have reduced the size and weight of many of the otherdisplay components. Today, one of the major limitations in furtherreducing the thickness and weight of the display is therefore the CCFLillumination system.

Light-emitting diode (“LED”) technology offers attractive alternativesto the CCFL. LEDs are much thinner than the CCFL and do not require manyof the weighty power supply systems of the CCFL. Compared to backlightsusing CCFLs, backlights with LEDs have many benefits, including lighterweight, higher brightness, higher color purity, larger color gamut,longer lifetime, and mercury-free composition. However, while a singleCCFL can light an entire display, multiple LEDs are needed to lightcomparable displays.

A challenge with utilizing multiple LEDs, particularly when distributedin large arrays, is maintaining uniformity of color throughout the largenumber of LEDs. The color balance and spectra of the LEDs is governed bynumerous factors such as manufacturing variances and the LEDphosphorescence. For example, white LEDs are often actually blue LEDswith a complimentary yellow phosphor dot on the front of the LED.Depending upon manufacturing precision (and thus, related manufacturingcosts), actual colors may therefore vary from, for example, slightlyblue to slightly pink, often following a distribution curve in whichmany of the LEDs vary from the desired white point color. This can havea negative impact on the color uniformity of LCD displays.Understandably, reducing or compensating for such variability increasescosts and complexity significantly as the number of LEDs increases inlarger display configurations and environments.

One solution is to select and utilize only those LEDs that provide thedesired white point color. Such a solution, however, causes costs to bevery high since only a fraction of the LED production can be utilized.

Another solution is to compensate for LED color variations, such as bymatching LEDs to one another and then filtering the light output toadjust the color to the desired white point color. This reduces theoverall cost of the LEDs since most or all of the LEDs can be utilized.However, the additional color filters represent costly additionalphysical elements, oftentimes requiring a large number of availablefilter colors of finely varying shades and gradations. It can alsoincrease the thickness of the display. An additional disadvantage isthat such filters absorb light, causing the net brightness of the LEDlight sources to be reduced.

Thus, if LEDs are to become a viable alternative to CCFLs, an economicaland practical solution must be found to utilize a large number ofnon-matching LEDs while maintaining uniformity of color in the displaypanels in which the LEDs are utilized.

In view of ever-increasing commercial competitive pressures, increasingconsumer expectations, and diminishing opportunities for meaningfulproduct differentiation in the marketplace, it is increasingly criticalthat answers be found to these problems. Moreover, the ever-increasingneed to save costs, improve efficiencies, improve performance, and meetsuch competitive pressures adds even greater urgency to the criticalnecessity that answers be found to these problems.

Solutions to these problems have been long sought but prior developmentshave not taught or suggested any solutions and, thus, solutions to theseproblems have long eluded those skilled in the art.

SUMMARY OF THE INVENTION

The present invention provides an LED backlight method and apparatus fordisplay systems. A plurality of light emitting diodes having differentwhite point colors is provided. At least two of the light emittingdiodes having different white point colors are selected to produce alight of a predetermined white point color when the light outputs of theselected light emitting diodes are mixed. The selected light emittingdiodes are mounted on a display panel in a predetermined order atspatially distributed positions for mixing their light outputs toproduce the light of the predetermined white point color to illuminatethe display panel with the light of the predetermined white point color.

Certain embodiments of the invention have other aspects in addition toor in place of those mentioned above. The aspects will become apparentto those skilled in the art from a reading of the following detaileddescription when taken with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a portable computer incorporating a panelilluminated by LEDs selected and mounted according to the presentinvention;

FIG. 2 is an enlarged detail from FIG. 1 of the panel with the removablelight strip;

FIG. 3 is an enlarged detail from FIG. 2 of the removable light strip;

FIG. 4 is a representative LED color binning chart;

FIG. 5 is a schematic illustration of a light distribution system for anedge-lit backlight for a panel;

FIG. 6 is a brightness map comparison of a color simulation according toan embodiment of the present invention;

FIG. 7 shows brightness contribution details of the near field in FIG.6;

FIG. 8 illustrates optimized LED color mixing with eight color binsaccording to an embodiment of the present invention;

FIGS. 9A and 9B show, respectively, the simulated color distributionuniformity with optimized LED order results in the near field and thefar field for optimization that minimizes the distance from the centerpoint;

FIGS. 10A and 10B show, respectively, the simulated color distributionuniformity with optimized LED order results in the near field and thefar field for optimization that minimizes the distance from the shiftedBlack-Body curve;

FIG. 11 illustrates simulated worst color differences for an eight-binpanel as a function of the normalized distance d/L from the LEDs in theactive area;

FIGS. 12A, 12B, 13A, and 13B illustrate embodiments of the presentinvention with optimized six color bin configurations in the near field;

FIGS. 14A and 14B illustrate embodiments of the present invention withoptimized four color bin configurations in the near field;

FIGS. 15A and 15B illustrate worst color differences for severalfour-bin panel configurations as a function of the normalized distanced/L from the LEDs;

FIG. 16 shows an embodiment for a four-bin simulation configuration thatutilizes eight actual color bins;

FIG. 17 shows the color uniformity in a representative 13.3″ LCD modulefor an optimized 8-bin LED mixing backlight unit according to anembodiment of the present invention;

FIG. 18 shows the color uniformity in a representative 13.3″ LCD modulefor an optimized 4-bin LED mixing backlight unit according to anembodiment of the present invention;

FIG. 19 is a flow chart for an embodiment of a color simulationaccording to the present invention; and

FIG. 20 is a flow chart of an LED backlight method for display systemsin accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following embodiments are described in sufficient detail to enablethose skilled in the art to make and use the invention. It is to beunderstood that other embodiments would be evident based on the presentdisclosure, and that system, process, or mechanical changes may be madewithout departing from the scope of the present invention.

In the following description, numerous specific details are given toprovide a thorough understanding of the invention. However, it will beapparent that the invention may be practiced without these specificdetails. In order to avoid obscuring the present invention, somewell-known circuits, system configurations, and process steps are notdisclosed in detail.

Similarly, the drawings showing embodiments of the system aresemi-diagrammatic and not to scale and, particularly, some of thedimensions are for the clarity of presentation and are exaggerated inthe drawing FIGs. Likewise, although the views in the drawings for easeof description generally show similar orientations, this depiction inthe FIGs. is arbitrary for the most part. Generally, the invention canbe considered, understood, and operated in any orientation.

In addition, where multiple embodiments are disclosed and describedhaving some features in common, for clarity and ease of illustration,description, and comprehension thereof, similar and like features one toanother will ordinarily be described with like reference numerals.

For expository purposes, terms, such as “above”, “below”, “bottom”,“top”, “side” (as in “sidewall”), “higher”, “lower”, “upper”, “over”,and “under”, are defined with respect to the back of the display deviceexcept where the context indicates a different sense. The term “on”means that there is direct contact among elements.

Referring now to FIG. 1, therein is shown a portable computer 100 havinga base 102 attached to a screen or panel 104. In this embodiment, thebase 102 contains most of the components of the portable computer 100such as a keyboard 106, a trackpad 108, a disk drive (not shown), andthe motherboard (not shown). The panel 104 is illuminated bylight-emitting diodes (“LEDs”) (not shown, but see the LEDs 306 in FIG.3) selected and mounted according to the present invention.

Referring now to FIG. 2, therein is shown a close up of the panel 104.In this embodiment the panel 104 is a liquid crystal display (“LCD”).The panel 104 is electrically connected by suitable connectors (notshown, but see the power feed contact 318, FIG. 3) to a removable lightstrip 202. The removable light strip 202, which is shown partiallyinserted into the panel 104, illuminates the panel 104 from the base orbottom thereof. When fully inserted into the panel 104, the removablelight strip 202 is retained therein by a suitable retaining means, suchas a detent, latch, and so forth (not shown).

The panel 104 includes a bezel 204 that surrounds the active area 206 ofthe panel 104. The active area 206 is the illuminated portion in whichthe images are displayed, the removable light strip 202 being locatedbehind the bezel 204 below the active area 206. The region of the activearea 206 nearer the removable light strip 202, toward the bottom of thepanel 104, then constitutes the near field 208 of the active area 206.Similarly, the region of the active area 206 farther from the removablelight strip 202, toward the top of the panel 104, constitutes the farfield 210 of the active area 206.

Referring now to FIG. 3, therein is shown a close up of the removablelight strip 202. In this embodiment, side firing LEDs 306 are mounted onand electrically connected to one another on a flex 308. The flex 308 isa conventional flexible medium onto which electrical components andconnections are mounted. The LEDs 306 are spaced a distance 310 fromeach other. The distance 310 is equal to or greater then the length ofthe LEDs 306 and forms alignment areas 312. In this embodiment, the flex308 has a fold 314 where the flex 308 is folded back on itself to form afolded flex 316. The folded flex 316 has a power feed contact 318 thatconnects (not shown) to the panel 104 (FIG. 2) when inserted into thepanel 104. The folded flex 316 is encased in an assembly housing 320.The assembly housing 320 provides support for the folded flex 316, theLEDs 306, and the power feed contact 318.

LEDs, such as the LEDs 306, are point light sources. Therefore whenilluminating a panel with LEDs, it is generally preferable to use manyspatially distributed LEDs to efficiently and economically obtainuniform illumination of the panel. Desired brightness levels are muchmore readily and economically obtained as well through the use ofmultiple LEDs, since LED costs increase dramatically with higherindividual output light levels.

In order to achieve uniform and economical lighting across the panel104, the multiple LEDs 306 must effectively provide a uniform color. Thecolor balance and spectra of the LEDs 306 is limited by thephosphorescence. For example, white LEDs are often actually blue LEDswith a complimentary phosphor dot on the front of the LED. Dependingupon manufacturing precision (and thus, related manufacturing costs),actual colors may vary from, for example, slightly blue to slightlypink. Understandably, reducing or compensating for such variabilityincreases cost and complexity significantly as the number of LEDsincreases in larger display configurations and environments. Priorsolutions have therefore attempted to improve manufacturing processesand controls to produce highly uniform LEDs. Unfortunately, this hasresulted in high production costs and significant waste whennon-compliant LEDs could not be used and were rejected (thereby furtherincreasing costs).

Referring now to FIG. 4, therein is shown a representative LED colorbinning chart 400 or color bin map of LEDs such as from a commercial LEDmanufacturer. Using this or a similar chart, production LEDs are sortedinto groups of substantially matching colors, each group havingdifferent white point colors. That is, all LEDs having matchingproperties (e.g., color, brightness, forward voltage, flux, tint) thatfall within the same small region or “bin” 402 of the color binningchart 400 are sorted together with others having the same properties. Aspreviously suggested, only a few of the bins 402, located around aparticular desired white point color, have LEDs contained therein thathave been traditionally considered acceptable for production displays.LEDs sorted into other bins have been regarded as unacceptable orunusable, since the color differences are easily detected by the humaneye. Thus, in order to assemble a high color uniformity LED backlight,only one or limited color bins can be used in a particular displaymodel, which increases the difficulty and cost of the backlight units.

As is well known in the art, in the science of lighting there is acontinuum of colors of light that can be called “white”. One set ofcolors that deserve this description are the colors emitted, via theprocess called incandescence, by a black body at various relatively-hightemperatures. For example, the color of a black body at a temperature of2848 kelvins (“K”) matches the white light produced by domesticincandescent light bulbs. It is said that the color temperature of sucha light bulb is 2848 K. The white light used in theatre illumination hasa color temperature of about 3200 K. Daylight white light has a nominalcolor temperature of 5400 K (called equal energy white), but can varyfrom a cool slightly reddish hue up to a bluish 25,000 K. Not all blackbody radiation can be considered white light: the background radiationof the universe, to name an extreme example, is only a few kelvins andis quite invisible.

Standard whites are often defined with reference to the chromaticitydiagram of the International Commission on Illumination (“CIE”). Theseare the D series of standard illuminants. Illuminant D65, originallycorresponding to a color temperature of 6,500 K, is taken to representstandard daylight.

Computer displays often have a color temperature control, allowing theuser to select the color temperature (usually from a small set of fixedvalues) of the light emitted when the computer produces the electricalsignal corresponding to “white”. The RGB coordinates of white are 255255 255, regardless of the color temperature that is actually selectedfor white.

It has been unexpectedly discovered, according to the present invention,that color balance and uniformity across different production displayscan be maintained while using LEDs with wide variations in white pointcolors, thereby utilizing substantially all of the bins 402.

More particularly, according to the present invention, to achieve colorbalance and uniformity, LEDs with various white points are first sortedand binned into the bins 402, as before. The sorted LEDs within each bin402 produce substantially the same white point as others within the samegroup or bin 402. Different bins, in turn, each have their own,different white points since the actual production LEDs, in theaggregate, show slight color variations around the desired white pointcolor for the production displays. Then, as taught herein according toembodiments of the present invention, the LEDs from these various binsare successfully utilized by carefully selecting and physicallymounting, distributing, and locating particular LEDs having differentwhite point colors, from carefully selected bins 402, in selectedlocations in the display adjacent the display panel. The LEDs arearranged in a set order in spatially distributed positions for mixingtheir light outputs to provide complementary colors that combine in thedisplay to provide a light of the desired white point color forilluminating the entire display panel, including both the near field 208(FIG. 2) and the far field 210 (FIG. 2), with the light of thepredetermined white point color. The LEDs 306 selected from the bins 402in this fashion, and as more particularly described herein, thus havethe characteristics of having been selected from at least two differentsuch bins 402.

In prior configurations employing matching LEDs of the same color, thecolor of the LED light source was of course consistently the same acrossthe full display panel since all the LEDs matched. That condition doesnot necessarily obtain, however, when non-matching LEDs are utilized inphysically distributed locations along the edge of the display panel. Ittherefore becomes a non-trivial task, unexpectedly solved by the presentinvention, to configure and arrange such non-matching LEDs so that boththe near field 208 of the panel 104 (FIG. 2) and the far field 210 ofthe panel 104 consistently receive the same desired white point colorillumination.

The present invention is thus a new approach to achieving high coloruniformity LED backlight systems for LCD displays. By delicatelyselecting the order of the LED color bins 402 for the LEDs 306 (FIG. 3)that are assembled into the panel 104 backlight units, such as the lightstrip 202 (FIG. 2), the color difference on the backlight units can bewell balanced and high color uniformity can be achieved. As taughtherein, the specific bin 402 order of the LEDs 306 can be optimizedthrough computer color simulations.

Such a color simulation according to an embodiment of the presentinvention is described as follows. First, it is assumed that the colormixing between the different LED bins follows the color addition rules:

$\begin{matrix}{{x = {\sum\limits_{j}{I_{j}{x_{j}/{\sum\limits_{j}I_{j}}}}}}{y = {\sum\limits_{j}{I_{j}{y_{j}/{\sum\limits_{j}I_{j}}}}}}} & (1)\end{matrix}$

where I_(j), x_(j), and y_(j) are the brightness contribution and colorcoordinates in CIE 1931 of jth LED, respectively. This assumption isvalid for LEDs from the same manufacturer, since the spectra of suchLEDs are similar and the color difference is small.

The brightness contribution is assumed to be a Gaussian-type:

I(d)=exp[−d ²/(2σ²)]  (2)

where d is the horizontal distance from the LED and σ is a mixing powerparameter related to the distance L between LEDs, the properties of thebacklight system, and the position on the panel.

Referring now to FIG. 5, therein is shown a schematic illustration 500of a light distribution system for an edge-lit backlight for a panelsuch as the panel 104 (FIG. 2). In the illustrated light distributionsystem, light emitted from the LEDs 306 is incident on and mixes insidea light guide plate (“LGP”) 502. A brightness enhancement film (“BEF”)504 and diffuser film 506 collimate the light and provide high luminanceat near normal viewing angles, with the LGP 502, the BEF 504, and thediffuser film 506 all functioning as light mixing elements. The fartherthat the light travels in these elements, the better the mixing. Inother words, the mixing power increases with increasing distance fromthe light source.

Referring now to FIG. 6, therein is shown a brightness map comparison600 of a color simulation, according to an embodiment of the presentinvention, compared with real display systems. In this example, an LCDdisplay panel 104 was tested having a light source of 40 LEDs 306. Inthis panel, the LEDs 306 were located behind the bezel 204 spaced at adistance from the edge of the active area 206 similar or comparable tothe distance between adjacent LEDs 306. In other embodiments, the LEDs306 may be spaced from each other at distances generally greater or lessthan their distance from the active area 206 of the display panel 104,depending upon the color differences, color mixing efficiencies, anddesired performance specifications of the display. In this example, only8 LEDs 306′ in the 40 LED array are turned on (illuminated), alternatelyevery fifth LED, for testing purposes in order to reveal more clearlythe progression of the color mixing with increasing distance into thenear field 208 and the far field 210.

The measured brightness through the whole active area 206 of the panel104 is shown in FIG. 6 by isolumen lines 602. (The term “isolumen line”is a coined term defined and used herein to mean a line connectingpoints having the same luminous flux, analogous, for example, to the useof isobars on meteorological maps.) The closely spaced isolumen lines602 in the near field 208 show that the mixing power is low in the nearfield 208 close to the LEDs 306. On the other hand, the lack of isolumenlines 602 in the far field 210 shows that the mixing is very good in thefar field 210.

Referring now to FIG. 7, therein is shown brightness contributiondetails of a portion of the near field 208 from FIG. 6, comparing thebrightness contribution in the LCD panel 104 (FIG. 6) to a Gaussian-typesimulation. In FIG. 7, the horizontal distance is measured in a naturalunit; i.e., the distance between adjacent LEDs 306 (FIG. 6) is set tobe 1. The fitting curve is calculated using equation (2) with σ=1.0. Thesimulation agrees well with the real system.

In the far field 210 (as shown in FIG. 6), the brightness is veryuniform, which indicates that the mixing power is high and thebrightness contribution function (equation 2) should be slowly varied(larger σ).

Referring now to FIG. 8, therein is shown computer simulation results800, according to an embodiment of the present invention, that optimizesthe LED color mixing with eight color bins 402. Two criteria choices areshown: (1) minimum distance to the center point 802 in CIE 1976coordinates; (2) minimum distance to the shifted Black-Body curve 804 inCIE 1976 coordinates (it being noted that the shift can be restored bythe design of a color filter in the LCD panels).

Referring now to FIGS. 9A and 9B, therein are shown, respectively, thesimulated color distribution uniformity with optimized LED order resultsin the near field 208 (6=1) and the far field 210 (σ=5). Theoptimization method is to minimize the distance from the center point802 (expectation value). The optimal order of the LED bins 402 is (7 3 62 8 5 4 1)_(n). FIGS. 9A and 9B show that both the color differencesΔu′, Δv′ are smaller than 0.002, which are difficult for the human eyeto separate.

Referring now to FIGS. 10A and 10B, therein are shown, respectively, thesimulated color distribution uniformity with optimized LED order resultsin the near field 208 and the far field 210. The optimization method isto minimize the distance from the shifted Black-Body curve 804. In thiscase, the optimal order of the LED bins 402 is (7 4 5 8 3 6 2)_(n). Thecolor differences Δu′, Δv′ are also smaller than 0.002.

Referring now to FIG. 11, therein is shown the simulated worst colordifferences 1100 for an eight-bin panel 104 (FIG. 2) as a function ofthe normalized distance d/L from the LEDs 306 (FIG. 6) in the activearea 206 (FIG. 6). The worst color difference Δ is defined as Δ=√{squareroot over (Δu′²+Δv′²)} since the brightness is assumed to be nearlyuniform in the panel 104. FIG. 11 then shows that the worst colordifference falls into an acceptable range when the distance d in theactive area 206 is comparable to or greater than the distance L betweenadjacent LEDs.

The present invention includes embodiments in addition to the aboveeight-bin embodiments. It extends to other numbers of bins wherein theoptimal color difference is generally smaller than the color uniformityrequirements for the panel configuration at hand. Thus, referring now toFIGS. 12A, 12B, 13A, and 13B, therein are shown embodiments withoptimized six-bin configurations in the near field 208 (σ=1). Theoptimization method in FIGS. 12A and 12B is to minimize the distancefrom the center. The optimization method in FIGS. 13A and 13B is tominimize the distance from the Black-Body curve. FIGS. 12A, 12B, 13A,and 13B show that the color differences on the six-bin panels followsimilar behaviors to the eight-bin panels (above). In these particularsix bin embodiments, the color uniformity is actually slightly betterthan the optimized eight-bin configurations. The color differences Δu′,Δv′ are smaller than 0.001 when the distance in the active area iscomparable to or greater than the distance L between adjacent LEDs.Likewise, the theoretical average white point variation from panel topanel is expected to be smaller than 0.001 even though the individualsix color bins 402 are different.

Referring now to FIGS. 14A and 14B, therein is shown an optimizationembodiment with four color bins 402, in the near field 208. Theoptimization method is to minimize the distance from the center. Thecolor uniformity of this embodiment is actually slightly better thanthat of the optimized six bin embodiments above.

Referring now to FIGS. 15A and 15B, therein is shown the worst colordifferences for several four-bin panel configurations as a function ofthe normalized distance d/L from the LEDs 306 (FIG. 6) in the regionswhere the distance in the active area 206 (FIG. 6) is comparable to thedistance L between adjacent LEDs.

Referring now to FIG. 16, therein is shown an embodiment of the presentinvention for a four-bin simulation configuration 1600 that utilizeseight actual color bins 402 in the four-bin simulation. The eight colorbins are first split into four zones 1602, and the simulation accordingto the present invention is performed using each zone rather than eachbin. In one embodiment, in order to achieve a consistent far field whitepoint, one color bin 402 from each zone 1602 is accordingly picked toensure that the color deviation in the far field 210 (FIG. 2) is small.The LEDs selected from the bins 402 in the zones 1602 in this fashionthus have the characteristics of having been selected by picking onecolor bin 402 from each zone 1602.

Based upon these teachings, it will now be clear to persons of skill inthe art that other multi-bin embodiments can similarly be optimizedaccording to the present invention. For example, acceptable three bin orfive bin configurations can be built from acceptable four-binconfigurations by removing any one bin or adding any other bin, as longas the deviation from the center point at the far field is acceptableaccording to the target display parameters under consideration.

To illustrate this versatility, computer simulations as taught hereinoptimized the order of LEDs for 3-bin, 4-bin, 6-bin, and 8-bin colormixing and the corresponding LED backlight units for 13.3″ LCD modules.Table I (below) lists the measured white color coordinates (both CIE1931 and CIE 1976) of center points in 18 actual LCD modules constructedwith optimized LED color mixed backlight units in accordance therewith.The colors of the center points in these modules correspond with thecolors of the far field simulations. The measured far field data (x, y,u′, v′) confirms that the color on the panels is consistent (i.e., thatthe color variation from panel to panel is small). After such LED colormixing, the color difference Δ becomes less than 0.002 compared to thecolor differences of the LED color bins Δ˜0.008, which agrees with thesimulation results.

TABLE I Number of Panel Color Bins x y u′ v′ A 3 0.2861 0.3023 0.18900.4252 B 3 0.2850 0.3012 0.1886 0.4244 C 3 0.2846 0.3043 0.1872 0.4211 D3 0.2835 0.3010 0.1876 0.4221 E 4 0.2824 0.3023 0.1863 0.4192 F 4 0.28300.3009 0.1873 0.4214 G 4 0.2829 0.3030 0.1864 0.4194 H 4 0.2851 0.30410.1876 0.4221 I 4 0.2835 0.3029 0.1869 0.4205 J 4 0.2843 0.3026 0.18760.4220 K 4 0.2858 0.3033 0.1884 0.4239 L 4 0.2837 0.3011 0.1877 0.4223 M4 0.2840 0.3008 0.1880 0.4231 N 6 0.2847 0.3019 0.1881 0.4233 O 6 0.28260.3011 0.1869 0.4205 P 6 0.2843 0.3024 0.1877 0.4222 Q 8 0.2831 0.30250.1867 0.4202 R 8 0.2853 0.3030 0.1881 0.4233

Referring now to FIGS. 17 and 18, therein are shown the coloruniformities in representative 13.3″ LCD modules with optimized LEDmixing backlight units optimized according to embodiments of the presentinvention. FIG. 17 shows the color uniformity 1700 for an optimized8-bin unit; FIG. 18 shows the color uniformity 1800 for an optimized4-bin unit. In the near field 208, there is virtually no noticeablecolor difference between the LEDs, as predicted in the simulations.Additionally, the color uniformity over the panel is ˜0.005 with respectto the center point. This uniformity can be attributed to the brightnessuniformity and the angular dependence of the LED color.

Referring now to FIG. 19, therein is shown a flow chart 1900 for anembodiment of a color simulation, according to the present invention,for determining the order of the bins for selecting the LEDs from thebins for assembly cyclically in that order into a display panel, such asthe panel 104 (FIG. 2). Once thus determined, the LEDs are thenretrieved from the bins in that number order and assembled cyclically incorresponding order into the display panel light source, such as theremovable light strip 202 (FIG. 2) for the panel 104.

As depicted in FIG. 19, for N color bins, an initial order of the Ncolor bins is initiated, such as randomly, in a block 1902. Then, in ablock 1904, the near field and far field color differences of the orderof N color bins are calculated as described above. Next, two of thecolor bins are randomly permutated, in a block 1906. Then, in a block1908, the near field and far field color differences are againcalculated. Next, in a block 1910, a determination is made if the nearfield and far field color difference of the permutated bins is reducedfrom the near field and far field color difference of the order of Ncolor bins. Then, if the color difference was reduced, the permutationis accepted in a block 1912 and the procedure returns to block 1906. Ifthe color difference was not reduced, the permutation is rejected in ablock 1914 and the procedure advances to block 1916. Then, in block1916, based upon the rejection of the permutation, a determination ismade if the calculation of the near field and far field color differenceis stabilized, and if not, the procedure returns to block 1908. If ithas stabilized, the procedure advances to block 1918. Then, in block1918, a determination is made if the near field and far field colorsmeet predetermined specifications. Then, if the near field and far fieldpredetermined color specifications are met, the optimal bin order, thenear field color, and the far field color are output in a block 1920.And if the near field and far field predetermined color specificationsare not met, an output is generated in a block 1922 that there is nooptimal bin order for this range of color bins, and optionallysuggesting that the range of the color bins be reduced. Accordingly, theLEDs, having different white point colors, that are thus selected willhave the characteristics of having been selected by means of the flowchart 1900.

Referring now to FIG. 20, therein is shown a flow chart 2000 of an LEDbacklight method for display systems in accordance with an embodiment ofthe present invention. The LED backlight method includes providing aplurality of light emitting diodes having different white point colors,in a block 2002; selecting at least two of the light emitting diodeshaving different white point colors to produce a light of apredetermined white point color when the light outputs of the selectedlight emitting diodes are mixed, in a block 2004; and mounting theselected light emitting diodes on a display panel in a predeterminedorder at spatially distributed positions for mixing their light outputsto produce the light of the predetermined white point color toilluminate the display panel with the light of the predetermined whitepoint color, in a block 2006.

It has been discovered that the present invention thus has numerousaspects.

A principle aspect that has been unexpectedly discovered is that thepresent invention readily and advantageously enables essentially all ofthe bins of the white LEDs to be used.

Another important aspect is that all the LEDs can be used whilemaintaining uniform color output across the entire display production.

Another aspect, accordingly, is that it is now possible to meet coloruniformity requirements by mixing LEDs from various color bins.

Yet another important aspect is that the full light output of the LEDscan be delivered to the display panels since filters to compensate foroff-white LED outputs are not needed.

Another important aspect is that the full color range that is availableto the display panel is preserved because the LCD panel is notcompromised by the need to generate a color shift for the LED lightsource.

Still another aspect is that by carefully selecting the order of the LEDcolor bins for assembling the LEDs in backlight units, the colordifference on the backlight units can be well balanced and high coloruniformity LED backlights can be achieved.

Yet another important aspect of the present invention is that itadvantageously and unexpectedly relaxes the restricted color binrequirement for LED backlights and lowers the costs of LED backlightunits.

Still another valuable aspect of the present invention is that it can beeffectively applied to and used for both large numbers and small numbersof bins.

Another significant aspect is that the panels not only show high coloruniformity over the panels, but also have a consistent color from panelto panel.

Yet another important aspect of the present invention is that itvaluably supports and services the historical trend of reducing costs,simplifying systems, and increasing performance.

These and other valuable aspects of the present invention consequentlyfurther the state of the technology to at least the next level.

Thus, it has been discovered that the display system of the presentinvention furnishes important and heretofore unknown and unavailablesolutions, capabilities, and functional aspects for utilizing virtuallythe full range of production LEDs. The resulting processes andconfigurations are straightforward, cost-effective, uncomplicated,highly versatile and effective, can be surprisingly and unobviouslyimplemented by adapting known technologies, and are thus readily suitedfor efficiently and economically manufacturing display devices. Theresulting processes and configurations are straightforward,cost-effective, uncomplicated, highly versatile, accurate, andeffective, and can be implemented by adapting known components forready, efficient, and economical manufacturing, application, andutilization.

While the invention has been described in conjunction with a specificbest mode, it is to be understood that many alternatives, modifications,and variations will be apparent to those skilled in the art in light ofthe aforegoing description. Accordingly, it is intended to embrace allsuch alternatives, modifications, and variations that fall within thescope of the included claims. All matters hithertofore set forth hereinor shown in the accompanying drawings are to be interpreted in anillustrative and non-limiting sense.

1. An LED backlight method for display systems, comprising: providing aplurality of light emitting diodes having different white point colors;selecting at least two of the light emitting diodes having differentwhite point colors to produce a light of a predetermined white pointcolor when the light outputs of the selected light emitting diodes aremixed; and mounting the selected light emitting diodes on a displaypanel in a predetermined order at spatially distributed positions formixing their light outputs to produce the light of the predeterminedwhite point color to illuminate the display panel with the light of thepredetermined white point color.
 2. The method as claimed in claim 1further comprising mounting the light emitting diodes along an edge ofthe display panel spaced from the active area of the display panel. 3.The method as claimed in claim 2 wherein the light emitting diodes arespaced from each other by a distance similar to their distance from theactive area of the display panel.
 4. The method as claimed in claim 2wherein the light emitting diodes are spaced from each other by adistance generally less than their distance from the active area of thedisplay panel.
 5. The method as claimed in claim 2 wherein the lightemitting diodes are spaced from each other by a distance generallygreater than their distance from the active area of the display panel.6. The method as claimed in claim 1: wherein the light emitting diodesare binned according to their white point colors; and further comprisingselecting the light emitting diodes from at least two different bins. 7.The method as claimed in claim 1 further comprising selecting at leastthree of the light emitting diodes, each having a different white pointcolor.
 8. The method as claimed in claim 1 further comprising: splittingthe different white point diodes into zones having multiple bins in eachzone, each bin having a different white point color; and picking onecolor bin from each zone.
 9. The method as claimed in claim 1 furthercomprising minimizing the near field and far field color differences.10. The method as claimed in claim 1 further comprising optimizing theLED order to minimize the distance from the center point.
 11. The methodas claimed in claim 1 further comprising optimizing the LED order tominimize the distance from the shifted Black-Body curve.
 12. The methodas claimed in claim 1 wherein selecting at least two of the lightemitting diodes having different white point colors further comprises:initiating an order of N color bins; then calculating the near field andfar field color difference of the order of N color bins; then randomlypermutating two of the color bins; then again calculating the near fieldand far field color difference; then determining if the again-calculatednear field and far field color difference is reduced from the near fieldand far field color difference of the order of N color bins; then, ifthe color difference is reduced, accepting the permutation and returningto the step of randomly permutating two of the color bins; otherwiserejecting the permutation; then, based upon the rejection of thepermutation, determining if the again-calculated near field and farfield color difference is stabilized, and if not, returning to the stepof again calculating the near field and far field color difference; thendetermining if the near field and far field colors meet predeterminedspecifications; then, if the near field and far field predeterminedcolor specifications are met, outputting the optimal bin order, the nearfield color, and the far field color; and then, if the near field andfar field predetermined color specifications are not met, outputtingthat there is no optimal bin order for this range of color bins.
 13. AnLED backlight for display systems, comprising: a plurality of lightemitting diodes having different white point colors; at least two of thelight emitting diodes having different white point colors being selectedto produce a light of a predetermined white point color when the lightoutputs of the selected light emitting diodes are mixed; a displaypanel; and the selected light emitting diodes being mounted on thedisplay panel in a predetermined order at spatially distributedpositions for mixing their light outputs to produce the light of thepredetermined white point color to illuminate the display panel with thelight of the predetermined white point color.
 14. The backlight asclaimed in claim 13 wherein the light emitting diodes are mounted alongan edge of the display panel spaced from the active area of the displaypanel.
 15. The backlight as claimed in claim 14 wherein the lightemitting diodes are spaced from each other by a distance similar totheir distance from the active area of the display panel.
 16. Thebacklight as claimed in claim 14 wherein the light emitting diodes arespaced from each other by a distance generally less than their distancefrom the active area of the display panel.
 17. The backlight as claimedin claim 14 wherein the light emitting diodes are spaced from each otherby a distance generally greater than their distance from the active areaof the display panel.
 18. The backlight as claimed in claim 13: furthercomprising light emitting diodes that are binned according to theirwhite point colors; and wherein the selected light emitting diodes havethe characteristics of being selected from at least two different suchbins.
 19. The backlight as claimed in claim 13 further comprising atleast three of the light emitting diodes, each having a different whitepoint color.
 20. The backlight as claimed in claim 13: furthercomprising different white point diodes that are split into zones havingmultiple bins in each zone, each bin having a different white pointcolor; and wherein the selected light emitting diodes have thecharacteristics of being selected by picking one color bin from eachzone.
 21. The backlight as claimed in claim 13 wherein the selectedlight emitting diodes minimize the near field and far field colordifferences.
 22. The backlight as claimed in claim 13 wherein theselected light emitting diodes optimize the LED order by minimizing thedistance from the center point.
 23. The backlight as claimed in claim 13wherein the selected light emitting diodes optimize the LED order byminimizing the distance from the shifted Black-Body curve.
 24. Thebacklight as claimed in claim 13 wherein at least two of the selectedlight emitting diodes having different white point colors have thecharacteristics of having been selected by: initiating an order of Ncolor bins; then calculating the near field and far field colordifference of the order of N color bins; then randomly permutating twoof the color bins; then again calculating the near field and far fieldcolor difference; then determining if the again-calculated near fieldand far field color difference is reduced from the near field and farfield color difference of the order of N color bins; then, if the colordifference is reduced, accepting the permutation and returning to thestep of randomly permutating two of the color bins; otherwise rejectingthe permutation; then, based upon the rejection of the permutation,determining if the again-calculated near field and far field colordifference is stabilized, and if not, returning to the step of againcalculating the near field and far field color difference; thendetermining if the near field and far field colors meet predeterminedspecifications; then, if the near field and far field predeterminedcolor specifications are met, outputting the optimal bin order, the nearfield color, and the far field color; and then, if the near field andfar field predetermined color specifications are not met, outputtingthat there is no optimal bin order for this range of color bins.